/**
 * Implement a basic calculator to evaluate a simple expression string.
 * The expression string contains only non-negative integers, +, -, *, / operators and empty spaces . 
 * The integer division should truncate toward zero.
 * You may assume that the given expression is always valid.
 * Some examples:
 * "3+2*2" = 7
 * " 3/2 " = 1
 * " 3+5 / 2 " = 5
 */
/**
 * @author I321035
 *
 */
package problem227_Basic_Calculator_II;